Revealing mistake: Ken is killing Diane by stabbing her with the knife. You can see that Ken is only stabbing the floor next to her.
Revealing mistake: Diane has a bloody wound on her left hip, before the killer actually cuts her with the drill.
Slumber Party Massacre III (1990)
2 revealing mistakes - chronological order
Directed by: Sally Mattison
Starring: Brittain Frye, Hope Marie Carlton, Michael Harris, Brandi Burkett, David Greenlee, Keely Christian, Maria Claire
Genres: Horror
Continuity mistake: The front door changes in the interior view of Jackie's house a couple of times.
Jackie: Oh, my God, the basement! I forgot there's a window in there! Give me that poker.
Diane: Jackie, you're not going down there.
Duncan: Besides, they're tongs.